This invention relates to polyurea foams. More specifically, it concerns compositions and processes useful in preparing polyurea foams.
Polyurea foams are advantageously prepared using amine terminated polyethers. Such foams are well known in the art and are taught, for instance, in U.S. Pat. Nos. 3,838,076 to Hotchkiss et al.; 4,396,729 to Dominguez et al.; 4,433,067 to Rice et al.; 4,444,910 to Rice et al.; 4,474,901 to Dominguez; 4,530,941 to Turner et al.; 4,642,320 to Turner et al.; 4,588,840 to Gurgiolo; 4,732,919 to Grigsby it al.; European Patent Nos. 81,701 and 255,371; copending U.S. application Ser. No. 170,971 filed Mar. 21, 1988.
Polyurea foams have many uses. They are generally advantageous when relatively high load bearing strengths are needed. In flexible foams, the advantages of polyurea formulations over polyurethane formulations that produce similar load bearing characteristics frequently include lower isocyanate index, lower viscosity because copolymer polyols are often unnecessary, and less foam shrinkage since less crosslinker is generally required. Additionally, polyurea foams offer greater latitude in the amount of water that can be used without marked shrinkage and generally require crushing after molding less often than do polyurethane foams.
Flexible polyurea foams are used in a wide variety of applications, particularly as cushioning such as in automobile seats, headrests, dashboards and the like, in furniture, bedding, carpet padding, packaging, toys and the like. Rigid polyurea foams are particularly useful in insulation, for instance for vessels, pipelines, ice chests, appliances, buildings and the like.
Formation of polyurea foams typically requires a blowing or nucleating agent to achieve a CELLULAR structure and/or a preselected density. Frequently, such foams are water-blown, but often water alone is insufficient to achieve a preselected density. Using water alone may also be disadvantageous when the water required would increase the exotherm of a foaming mass sufficiently to degrade the foam. Chlorofluorocarbons have proven useful as blowing agents in polyurea foams, but use of alternative blowing agents is sometimes favored.
There have been some teachings of using compounds which may liberate carbon dioxide on heating to contribute to the blowing of polyurethane foams. For instance, U.S. Pat. No. 4,417,002 discloses use of certain salts of formic acid and a weak organic base to liberate carbon dioxide and carbon monoxide for foam formation. U.S. Pat. No. 3,635,908 teaches the addition of certain polyamine carbamates to certain polyurethane formulations to form thermoplastic polyurethane-ureas which are extruded under specified conditions. U.S. Pat. Nos. 4,077,920 and 4,500,656 disclose certain polyurethane foams prepared using certain amine carbamates of amines having alcoholic hydroxy groups. U.S. Pat. No. 4,284,728 discloses certain high resiliency polyurethane foam formulations wherein acids or carbon dioxide are used to stabilize certain reactive amines. U.S. Pat. Nos. 4,499,038 and 4,645,630 disclose preparation of certain polyurea-based MICROCELLULAR moldings prepared by reaction injection molding (RIM) processes using certain aliphatic amine compounds having ammonium carbamate groups.
The above patents disclose processes or compositions by or from which certain amounts of potentially available carbon dioxide may be released for blowing at certain temperatures. Several of the processes and compositions require that certain amines, often amines with hydroxyl groups, be added to higher molecular weight active hydrogen compounds in specific polyurethane formulations. Addition of such compounds, which generally behave as chain extenders, increases the hard segments in a polyurethane foam and changes the physical properties thereof. Frequently, the load bearing strength is increased while tensile, tear and elongation are lowered. Since the amount of carbon dioxide available is limited by the number of amine groups reacted therewith, obtaining more blowing from carbon dioxide requires use of more of these compounds and, therefore, more change in physical properties.
It would be desirable to use, as a blowing agent, a material which would form, in the course of polyurea formation, a gas suitable for foaming and a compound reactive in polyurea formation. Preferably the compound would be one normally used in a polyurea formulation, rather than an added compound.